FIGS. 1, 2 and 3 illustrate a conventional device of this type, in which a preceding steel strip 1a and a subsequent steel strip 1b which are welding workpieces are clamped by clamp dies 2a, 2b and clamp bars 3a, 3b. Thereafter, a C-shaped shear frame 7 supporting an upper blade 4 and a lower blade 5 and having a pin guide hole 6 is moved to a welding position shown in FIG. 2 by a shear frame moving cylinder 8. The clamp bars 3a, 3b are moved up and down by clamp cylinders 10a, 10b supported on the clamp supporting frame 9, thereby rigidly holding the preceding and subsequent steel strips 1a, 1b. The clamp supporting frame 9 is supported at its opposite ends by a pin support frame 11 and a clamp frame 12, and the clamp dies 2a, 2b are fixed on the pin supporting frame 11, the clamp frame 12, and a common base 13. On the top face of the common base 13 is a rail 14 for positioning and guiding the shear frame 7. The clamp bar 3a has fixed thereon a rail 15 on which a welding torch moves, and a laser welding torch 16 moves rightward in FIG. 1 during the welding operation.
Cutting of the welding workpieces is simultaneously achieved while holding the shear frame 7 at the welding position shown in FIG. 2 by cutting, in the manner shown in FIG. 3, the ends of the preceding and subsequent steel strips 1a, 1b with the upper and the lower blades. In order to resist the cutting reaction force during this cutting operation, a pin 17 mounted on the pin supporting frame 11 is inserted by a cylinder 18 into the pin guide hole 6 formed in the shear frame 7. Then, the cutting of the preceding and the subsequent steel strips 1a, 1b is achieved, and thereafter the shear frame 7 recedes back to the position shown in FIG. 1 by a shear frame moving cylinder 8.
Then, in the position in which the preceding steel strip 1a is moved to the left in FIG. 3 and in which the cut faces of the preceding and the subsequent steel strips 1a and 1b engage with each other without any gap therebetween, the laser welding torch 16 emits a laser beam while moving at a constant speed to the right in FIG. 1 to form a weld.
However, the conventional cutting device of the construction as described above has been disadvantageous in that, since the pin supporting frame 11 on which the pin 17 is secured and the shear frame 7 in which the pin guide hole 6 is formed are independent from each other, the precision positioning of the pin 17 and the pin guide hole 6 is extremely difficult. Furthermore, since the pin supporting frame 11 for resisting the cutting reaction force (about 70 tons with a thickness of 4.5 mm) is mounted on the common base 13, the pin supporting frame 11 is inevitably very large.